Anisotropic electroconductive films in each of which an electroconductive particle is dispersed in an insulating adhesive are used as a connection member for simply making connection between a liquid crystal display and a semiconductor chip or a TCP (Tape Carrier Package), connection between an FPC (Flexible Printed Circuit) and a TCP, or connection between an FPC and a printed wiring board. For example, anisotropic electroconductive films are widely used for making connection between a liquid crystal display of a laptop computer or a cellular phone and a control IC, and are also used for mounting flip chips in such a way that semiconductor chips are directly mounted on printed boards or flexible wiring boards (Patent Documents 1, 2 and 3).
In the field concerned, in these years, connected wiring patterns and electrode sizes are increasingly miniaturized, and conventional anisotropic electroconductive films in which electroconductive particles are randomly dispersed come to be hardly capable of making such connection as described above with high connection reliability. In other words, when the electroconductive particle density is increased for the purpose of connecting microarea electrodes, the electroconductive particles are agglomerated, and consequently insulation between adjacent electrodes cannot be maintained. Conversely, when the electroconductive particle density is decreased for the purpose of maintaining such insulation, some electrodes are not connected, and consequently it has been accepted that it is difficult to cope with miniaturization while connection reliability is being maintained (Patent Document 4).
On the other hand, an attempt has been made to cope with micropattern connection by using an anisotropic electroconductive film in which by making the thickness of an insulating film smaller than the electroconductive particle diameter, the electroconductive particles are exposed to the front and back sides of the film (Patent Document 5). However, when the thickness of the insulating film is smaller than the particle diameter, air pools are formed in the connection area and consequently adhesion failure tends to be caused. For the purpose of preventing such failure, on one side of the insulating film, an insulating adhesive layer is further formed. In such as case, for the purpose of developing the connection reliability in the connection of microarea connection, the thickness of the insulating film is preferably as small as possible. However, when the thickness of the insulating film is small, the electroconductive particles tend to be detached during production process or during use, hence connection defects are caused, and consequently, the reduction of the thickness of the insulating film is limited.    Patent Document 1: JP-A-03-107888    Patent Document 2: JP-A-04-366630    Patent Document 3: JP-A-61-195179    Patent Document 4: JP-A-09-312176    Patent Document 5: JP-A-07-302666